The present invention relates to an ignition timing control apparatus for gasoline engines, etc., and more particularly to an ignition timing control apparatus having a knock control function.
With gasoline engines, etc., attempts to enhance their performance often lead to many detrimental effects due to engine knocking.
Thus, devices of the type employing a sensor for detecting knocking so that upon occurrence of knocking the ignition timing is immediately retarded to prevent the knocking, that is, so-called knock control devices, have recently come into wide use.
With the known type of knock control devices, when knocking occurs, the ignition timing is retarded a predetermined amount and then the ignition timing is gradually restored to the basic ignition timing providing the same amount of ignition timing retard for all the cylinders of the engine (e.g., Japanese Patent Unexamined Publication No. 57-38667).
Also, with gasoline engines, etc., the knocking ignition timing differs considerably among the cylinders depending on the engine with the result that in the case of the known knock control device, despite the knock control being performed, the cylinders having a high knocking tendency always cause knocking.
Assuming now that the basic ignition timing is set in relation to the cylinder having the highest knocking tendency, it is impossible to ensure a satisfactory engine performance. On the other hand, if the basic ignition timing is set in relation to the cylinder having the lowest knocking tendency, the cylinders having the higher knocking tendency always remain in the knocking zone so that these cylinders always cause middle or heavy knocking during the interval between the time that the ignition timing is retarded and the time that the ignition timing is restored to the basic ignition timing. Note that the terms middle knock and heavy knock indicate degrees of knocking, that is, middle knock designates a medium degree of knocking and heavy knock designates a considerably high degree of knocking. Also, a light degree of knocking is called light knock and a very low degree of knocking is referred to as a trace knock.
Thus, the conventional knock control devices are disadvantageous in that the variations in knocking characteristics among the cylinders are not accommodated and the desired engine performance is not ensured fully.
This type of knock control device is disclosed for example in Japanese Patent Unexamined Publication No. 58-167880.
The known knock control devices are also disadvantageous in that, if there are variations in knock intensity among the cylinders of an engine, there is the danger of failing to detect knocking with respect to some cylinders and thus a failure to satisfactorily prevent the occurrence of knocking. Moreover, the engine and sensor undergo aging so that it has been difficult in the past to ensure satisfactory detection of knocking and hence prevent the occurrence of knocking.